A long-standing dilemma in tumor immunology is the ability of solid tumor cells to escape immune surveillance despite demonstrable antitumor T-cell response. Primarily, the immune evasion mechanism of tumor has been evaluated in the context of expression of immunosuppressive bio-molecules viz., IL-10, transforming growth factor-b (TGF-b), indoleamine-2,3-deoxygenase (IDO), macrophage colony stimulating factor (M-CSF), arginase, prostaglandin E2 (PGE2), cyclooxygenase-2 (COX2) and nitric-oxide synthase 2 (NOS2), IL-6, chemokine CXCL12 and the like, that inhibit the function of dendritic cells (DC) and T cells. The increased expression of death inducing molecules (FasL & TRAIL), which induces apoptosis in tumor infiltrating T cells, has also been elucidated to explain the mechanism by which tumors evade the immune system.
The migration of immune cells to a target site is a major step in eliciting the immune response against tumor cell. Chemotaxis, or the oriented movement of a cell in response to a chemical agent, is a complex and highly integrated process. The movement can be positive (toward) or negative (away) from a chemical gradient. Movement toward an agent or stimulus is termed positive chemotaxis (i.e., the agent or stimulus is chemoattractive for the cell), while movement away from an agent or stimulus is termed negative chemotaxis (i.e., the agent or stimulus is chemorepulsive for the cell). It is believed that for both prokaryotes and eukaryotes, cells undergoing chemotaxis sense a change in agent concentration and, thereby, move in response to the concentration gradient. Chemoattraction (CA) and chemorepulsion (CR) are therefore properties of the agent or stimulus, while chemotaxis is a property of cells.
The present inventors have discovered proteins which are expressed (secreted) by tumor cells which keep anti-tumor T cells (CD4 & CD8), neutrophils, NK cells at the bay while concomitantly recruiting regulatory T cells at tumor sites and thus mediating evasion of the immune response. It would be advantageous to identify these proteins released from cancer cells that induce negative chemotaxis of immune cells and/or inhibit the activity of these proteins in order to induce positive chemotaxis of immune cells toward cancer cells.